how do u get rid of gnats in the chicken run?

We have had a lot of gnats and flies in the chicken run. What is the best way to get rid of them? We have gravel in the run to help with the moisture. I was hoping this would also help with the smell, but we have a lot of little gnats .

Mom to a teenager, a preteen, and a "thinks he's a teen", wife to the best man on the planet, and owner of 2 German Shepherds, 1 criminally insane cat, 2 adorable orange kittens, and 7 hens: 1BO, 1BSL, 1 golden comet, 1 delaware, 1 BR, and 2 EE's.

A people that values its privileges above its principles will soon lose both.

Mom to a teenager, a preteen, and a "thinks he's a teen", wife to the best man on the planet, and owner of 2 German Shepherds, 1 criminally insane cat, 2 adorable orange kittens, and 7 hens: 1BO, 1BSL, 1 golden comet, 1 delaware, 1 BR, and 2 EE's.

A people that values its privileges above its principles will soon lose both.

I've been noticing a lot of flies in my run (sand) since the weather has been warmer. I did some searches on here and came up with something called "Dry Stall" that people sprinkle in their runs and coops. I think it helps dry the poo quickly so it doesn't attract bugs. It's fairly inexpensive at $10-$15 for a 40 pound bag, but I can't find it with a reasonable shipping price, so I'm going to try and find it locally. I hope this helps and that it works!! Any other ideas would be great.
Thanks for the info, birdaholic. I'm going to try that tomorrow!